Re: [PATCH v1 06/11] arm_mpam: Use __ris_msmon_read() for saving MBWU state

[Gavin Shan <gshan@redhat.com>]

On 7/10/26 9:55 PM, Ben Horgan wrote:
> mbwu_save_mbwu_state() reads the MBWU counters and adds that to a saved
> correction value. However, the type of counter to read is determined by the
> RIS rather than the class and overflow is not taken into account. Fix this
> and mitigate against further divergence by using the same helper as used
> for user reads, __ris_msmon_read().
> 
> Fixes: 41e8a14950e1 ("arm_mpam: Track bandwidth counter state for power management")
> Signed-off-by: Ben Horgan <ben.horgan@arm.com>
> ---
>   drivers/resctrl/mpam_devices.c | 33 +++++++++++++++++++++------------
>   1 file changed, 21 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
> index 222fc248067e..a49f426aefc0 100644
> --- a/drivers/resctrl/mpam_devices.c
> +++ b/drivers/resctrl/mpam_devices.c
> @@ -1029,12 +1029,6 @@ struct mon_read {
>   	bool				waited_timeout;
>   };
>   
> -static bool mpam_ris_has_mbwu_long_counter(struct mpam_msc_ris *ris)
> -{
> -	return (mpam_has_feature(mpam_feat_msmon_mbwu_63counter, &ris->props) ||
> -		mpam_has_feature(mpam_feat_msmon_mbwu_44counter, &ris->props));
> -}
> -
>   static u64 mpam_msc_read_mbwu_l(struct mpam_msc *msc)
>   {
>   	int retry = 3;
> @@ -1687,6 +1681,7 @@ static int mpam_save_mbwu_state(void *arg)
>   	struct mpam_msc_ris *ris = arg;
>   	struct msmon_mbwu_state *mbwu_state;
>   	struct mpam_msc *msc = ris->vmsc->msc;
> +	struct mpam_class *class = ris->vmsc->comp->class;
>   
>   	for (i = 0; i < ris->props.num_mbwu_mon; i++) {
>   		mbwu_state = &ris->mbwu_state[i];
> @@ -1702,18 +1697,32 @@ static int mpam_save_mbwu_state(void *arg)
>   		cur_flt = mpam_read_monsel_reg(msc, CFG_MBWU_FLT);
>   		cur_ctl = mpam_read_monsel_reg(msc, CFG_MBWU_CTL);
>   
> -		if (mpam_ris_has_mbwu_long_counter(ris))
> -			val = mpam_msc_read_mbwu_l(msc);
> -		else
> -			val = mpam_read_monsel_reg(msc, MBWU);
> -
>   		cfg->mon = i;
>   		cfg->pmg = FIELD_GET(MSMON_CFG_x_FLT_PMG, cur_flt);
>   		cfg->match_pmg = FIELD_GET(MSMON_CFG_x_CTL_MATCH_PMG, cur_ctl);
>   		cfg->partid = FIELD_GET(MSMON_CFG_x_FLT_PARTID, cur_flt);
> -		mbwu_state->correction += val;
>   		mbwu_state->enabled = FIELD_GET(MSMON_CFG_x_CTL_EN, cur_ctl);
>   		mpam_mon_sel_unlock(msc);
> +
> +		if (mbwu_state->enabled) {
> +			struct mon_read mbwu_arg = {
> +				mbwu_arg.ris = ris,
> +				mbwu_arg.ctx = cfg,
> +				mbwu_arg.type = mpam_msmon_choose_counter(class),
> +				mbwu_arg.val = &val,
> +			};
> +
> +			val = 0;
> +			__ris_msmon_read(&mbwu_arg);
> +
> +			if (WARN_ON_ONCE(!mpam_mon_sel_lock(msc)))
> +				return -EIO;
> +
> +			mbwu_state->reset_on_next_read = true;
> +			if (!mbwu_arg.err)
> +				mbwu_state->correction = val;
> +			mpam_mon_sel_unlock(msc);
> +		}
>   	}

The unnecessary nested conditional statement can be avoided by
skipping the disabled MBWU state.

		if (!mbwu_state->enabled) {
			mpam_mon_sel_unlock(msc);
			continue;
		}

		mpam_mon_sel_unlock(msc);

		val = 0;
		mbwu_arg.ris = ris;
		mbwu_arg.ctx = cfg;
		mbwu_arg.type = mpam_msmon_choose_counter(class);
		mbwu_arg.val = &val
		__ris_msmon_read(&mbwu_arg);

		:
		:


>   
>   	return 0;

Thanks,
Gavin